Gnetophyta () is a division of plants (alternatively considered the subclass Gnetidae or order Gnetales), grouped within the
gymnosperm
The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό ...
s (which also includes
conifer
Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
s,
cycad
Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...
s, and
ginkgo
''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus within ...
s), that consists of some 70 species across the three
relict
A relict is a surviving remnant of a natural phenomenon.
Biology
A relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas.
Geology and geomorphology
In geology, a r ...
genera: ''
Gnetum
''Gnetum'' is a genus of gymnosperms, the sole genus in the family Gnetaceae within the Gnetophyta. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been ...
'' (
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Gnetaceae), ''
Welwitschia
''Welwitschia'' is a monotypic gymnosperm genus, comprising solely the distinctive ''Welwitschia mirabilis'', endemic to the Namib desert within Namibia and Angola. ''Welwitschia'' is the only living genus of the family Welwitschiaceae and orde ...
'' (family Welwitschiaceae), and ''
Ephedra Ephedra may refer to:
* Ephedra (medicine), a medicinal preparation from the plant ''Ephedra sinica''
* ''Ephedra'' (plant), genus of gymnosperm shrubs
See also
* Ephedrine
Ephedrine is a central nervous system (CNS) stimulant that is of ...
'' (family Ephedraceae). Fossilized pollen attributed to a close relative of ''Ephedra'' has been dated as far back as the
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
. Though diverse in the
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
, only three
families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...
, each containing a single
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
, are still alive today. The primary difference between gnetophytes and other gymnosperms is the presence of
vessel element
A vessel element or vessel member (also called trachea or xylem vessel) is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are typically found in angiosperms (flowering plants) but absent from most gy ...
s, a system of conduits that transport water within the plant, similar to those found in
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s. Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have brought this hypothesis into question.
Though it is clear they are all related, the exact evolutionary inter-relationships between gnetophytes are unclear. Some classifications hold that all three genera should be placed in a single
order (Gnetales), while other classifications say they should be distributed among three separate orders, each containing a single family and genus. Most morphological and molecular studies confirm that the genera ''Gnetum'' and ''Welwitschia'' diverged from each other more recently than they did from
''Ephedra''.
Ecology and morphology
Unlike most biological groupings, it is difficult to find many common characteristics between all of the members of the gnetophytes.
The two
common characteristics
Common may refer to:
Places
* Common, a townland in County Tyrone, Northern Ireland
* Boston Common, a central public park in Boston, Massachusetts
* Cambridge Common, common land area in Cambridge, Massachusetts
* Clapham Common, originally com ...
most commonly used are the presence of enveloping
bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...
s around both the
ovule
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the megasporangium), and the fe ...
s and
microsporangia
Microsporangia are sporangia that produce microspores that give rise to male gametophytes when they germinate. Microsporangia occur in all vascular plants that have heterosporic life cycles, such as seed plants, spike mosses and the aquatic fer ...
as well as a micropylar projection of the outer membrane of the ovule that produces a
pollination
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds ...
droplet,
[Judd, W.S.; Campbell, C.S.; Kellogg, E.A.; Stevens, P.F.; and Donoghue, M.J. (2008) Plant Systematics: A Phylogenetics Approach. 3rd ed. Sunderland, Massachusetts, USA: Sinauer Associates, Inc.] though these are highly specific compared to the similarities between most other plant divisions. L. M. Bowe refers to the gnetophyte genera as a "bizarre and enigmatic" trio
because, the gnetophytes' specialization to their respective environments is so complete that they hardly resemble each other at all. ''Gnetum'' species are mostly
woody vines in tropical forests, though the best-known member of this group, ''
Gnetum gnemon'',
[Wan T, Liu Z M, Li L F, et al. A genome for gnetophytes and early evolution of seed plants Nature plants, 2018, 4(2): 82.
] is a tree native to western
Malesia
Malesia is a biogeographical region straddling the Equator and the boundaries of the Indomalayan and Australasian realms, and also a phytogeographical floristic region in the Paleotropical Kingdom. It has been given different definitions. The ...
. The one remaining species of ''Welwitschia'', ''
Welwitschia mirabilis
''Welwitschia'' is a monotypic gymnosperm genus, comprising solely the distinctive ''Welwitschia mirabilis'', endemic to the Namib desert within Namibia and Angola. ''Welwitschia'' is the only living genus of the family Welwitschiaceae and ord ...
'', native only to the dry deserts of
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
and
Angola
, national_anthem = " Angola Avante"()
, image_map =
, map_caption =
, capital = Luanda
, religion =
, religion_year = 2020
, religion_ref =
, coordina ...
, is a ground-hugging species with only two large strap-like leaves that grow continuously from the base throughout the plant's life. ''Ephedra'' species, known as "jointfirs" in the United States, have long slender branches which bear tiny scale-like leaves at their nodes. Infusions from these plants have been traditionally used as a
stimulant
Stimulants (also often referred to as psychostimulants or colloquially as uppers) is an overarching term that covers many drugs including those that increase activity of the central nervous system and the body, drugs that are pleasurable and inv ...
, but
ephedrine
Ephedrine is a central nervous system (CNS) stimulant that is often used to prevent low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It is of unclear benefit in ...
is a
controlled substance
A controlled substance is generally a drug or chemical whose manufacture, possession and use is regulated by a government, such as illicitly used drugs or prescription medications that are designated by law. Some treaties, notably the Single C ...
today in many places because of the risk of harmful or even fatal
overdosing
A drug overdose (overdose or OD) is the ingestion or application of a drug or other substance in quantities much greater than are recommended. .
Fossil Gnetophyta
Knowledge of gnetophyte history through fossil discovery has increased greatly since the 1980s.
Gnetophyte fossils have been found that date from the
Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
and the
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
. Fossils dating back to the
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
have been found, though whether or not they belong to the gnetophytes is uncertain.
Overall, the fossil record is richest in the early
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
, with fossils of plants,
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
s, and
pollen
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
have been found that can clearly be assigned to the gnetophytes.
Classification
With just three well-defined genera within an entire division, there still is understandable difficulty in establishing an unambiguous interrelationship among them; in earlier times matters were even more difficult and we find for example Pearson in the early 20th century speaking of the
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
Gnetales, rather than the order.
[
] G.H.M. Lawrence referred to them as an order, but remarked that the three families were distinct enough to deserve recognition as separate orders.
[Lawrence, George Hill Mathewson. Taxonomy of vascular plants. Macmillan, 1951] Foster & Gifford accepted this principle, and placed the three orders together in a common class for convenience, which they called Gnetopsida.
[
] In general the evolutionary relationships among the
seed plants
A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...
still are unresolved, and the Gnetophyta have played an important role in the formation of
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
hypotheses. Molecular phylogenies of extant gymnosperms have conflicted with morphological characters with regard to whether the gymnosperms as a whole (including gnetophytes) comprise a
monophyletic group
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
or a
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
one that gave rise to angiosperms. At issue is whether the Gnetophyta are the
sister group
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and t ...
of angiosperms, or whether they are sister to, or nested within, other extant gymnosperms. Numerous fossil gymnosperm clades once existed that are morphologically at least as distinctive as the four living
gymnosperm
The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό ...
groups, such as Bennettitales, ''
Caytonia'' and the
glossopterids. When these gymnosperm fossils are considered, the question of gnetophyte relationships to other seed plants becomes even more complicated. Several hypotheses, illustrated below, have been presented to explain seed plant evolution. Morphological studies have supported a close relationship between Gnetophyta, Bennettitales and the
Erdtmanithecales.
Recent research by Lee, Cibrian-Jaramillo, ''et al.'' (2011) suggests that the Gnetophyta are a sister group to the rest of the gymnosperms,
[
] contradicting the anthophyte hypothesis, which held that gnetophytes were sister to the flowering plants.
Gnetifer hypothesis
In the gnetifer hypothesis, the gnetophytes are sister to the
conifer
Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
s, and the
gymnosperm
The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, ''Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμνό ...
s are a
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
group, sister to the angiosperms.The gnetifer hypothesis first emerged formally in the mid-twentieth century, when vessel elements in the gnetophytes were interpreted as being derived from
tracheid
A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through th ...
s with circular bordered pits, as in conifers.
[ It however only gained strong support with the emergence of molecular data in the late 1990s.][
][
] Although the most salient morphological evidence still largely supports the anthophyte hypothesis,some more obscure morphological commonalities between the gnetophytes and conifers lend support to the gnetifer hypothesis.These shared traits include: tracheids
A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through t ...
with scalariform pits with tori interspersed with annular thickenings, absence of scalariform pitting in primary xylem
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
, scale-like and strap-shaped leaves
A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
of ''Ephedra Ephedra may refer to:
* Ephedra (medicine), a medicinal preparation from the plant ''Ephedra sinica''
* ''Ephedra'' (plant), genus of gymnosperm shrubs
See also
* Ephedrine
Ephedrine is a central nervous system (CNS) stimulant that is of ...
'' and ''Welwitschia
''Welwitschia'' is a monotypic gymnosperm genus, comprising solely the distinctive ''Welwitschia mirabilis'', endemic to the Namib desert within Namibia and Angola. ''Welwitschia'' is the only living genus of the family Welwitschiaceae and orde ...
''; and reduced sporophyll
A sporophyll is a leaf that bears sporangia. Both microphylls and megaphylls can be sporophylls. In heterosporous plants, sporophylls (whether they are microphylls or megaphylls) bear either megasporangia and thus are called megasporophylls, or ...
s.[
]
Anthophyte hypothesis
From the early twentieth century, the anthophyte hypothesis was the prevailing explanation for seed plant
A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...
evolution, based on shared morphological characters between the gnetophytes and angiosperms. In this hypothesis, the gnetophytes, along with the extinct order Bennettitales
Bennettitales (also known as cycadeoids) is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales are among the most common Mesozoic seed plants ...
, are sister to the angiosperms, forming the "anthophytes".[ Some morphological characters that were suggested to unite the anthophytes include vessels in wood, net-veined leaves (in '']Gnetum
''Gnetum'' is a genus of gymnosperms, the sole genus in the family Gnetaceae within the Gnetophyta. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been ...
'' only), lignin
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
chemistry, the layering of cells in the apical meristem
The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...
, pollen
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
and megaspore
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These plants have two spore types, megaspores and microspores. Generally speaking, the megaspore, or large spore, germinates into a female gamet ...
features (including thin megaspore wall), short cambial initials, and lignin syringal groups.[
][
][
] However, most genetic studies, as well as more recent morphological analyses,[
] have rejected the anthophyte hypothesis.[
][
][
][
][
][
][
][
][
]
Several of these studies have suggested that the gnetophytes and angiosperms have independently derived characters, including flower-like reproductive structures and tracheid vessel elements, that appear shared but are actually the result of parallel evolution.
Gnepine hypothesis
The gnepine hypothesis is a modification of the gnetifer hypothesis, and suggests that the gnetophytes belong within the conifers as a sister group to the Pinaceae
The Pinaceae, or pine family, are conifer trees or shrubs, including many of the well-known conifers of commercial importance such as Cedrus, cedars, firs, Tsuga, hemlocks, larches, pines and spruces. The family is included in the order Pinales, ...
.[ According to this hypothesis, the conifers as currently defined are not a monophyletic group, in contrast with molecular findings that support its monophyly.][ All existing evidence for this hypothesis comes from molecular studies since 1999.] A 2018 phylogenomic study estimated the divergence between Gnetales and Pinaceae at around 241 millions of years ago, in the early Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
[ while a 2021 study placed it earlier, in the ]Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
.[
However, the morphological evidence remains difficult to reconcile with the gnepine hypothesis. If the gnetophytes are nested within conifers, they must have lost several shared derived characters of the conifers (or these characters must have evolved in parallel in the other two conifer lineages): narrowly triangular leaves (gnetophytes have diverse leaf shapes), ]resin
In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on natu ...
canals, a tiered proembryo
Plant embryonic development, also plant embryogenesis is a process that occurs after the fertilization of an ovule to produce a fully developed plant embryo. This is a pertinent stage in the plant life cycle that is followed by dormancy and germina ...
, and flat woody ovuliferous cone
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines con ...
scales.[ These kinds of major morphological changes are not without precedent in the ]Pinales
The order Pinales in the division Pinophyta, class Pinopsida, comprises all the extant conifers. The distinguishing characteristic is the reproductive structure known as a cone produced by all Pinales. All of the extant conifers, such as cedar, ...
, however: the Taxaceae
Taxaceae (), commonly called the yew family, is a coniferous family which includes six extant and two extinct genera, and about 30 species of plants, or in older interpretations three genera and 7 to 12 species.
Description
They are many-bran ...
, for example, have lost the classical cone of the conifers in favor of a single-terminal ovule, surrounded by a fleshy aril.[
]
Gnetophyte-sister hypothesis
Some partitions of the genetic data suggest that the gnetophytes are sister to all of the other extant seed plant groups.[
][
] However, there is no morphological evidence nor examples from the fossil record to support the gnetophyte-sister hypotheses.[
]
Fossil lineages
Ephedraceae
*'' Leongathia'' V.A. Krassilov, D.L. Dilcher & J.G. Douglas 1998 Koonwarra fossil bed, Australia, Early Cretaceous (Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...
)
*'' Jianchangia'' Yang, Wang and Ferguson, 2020 Jiufotang Formation
The Jiufotang Formation ( Chinese: 九佛堂组, pinyin: ''jiǔfótáng zǔ'') is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see ...
, China, Early Cretaceous (Aptian)
*'' Eamesia'' Yang, Lin and Ferguson, 2018 Yixian Formation
The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...
, China, Early Cretaceous (Aptian)
*'' Prognetella'' Krassilov et Bugdaeva, 1999 Yixian Formation, China, Early Cretaceous (Aptian) (initially interpreted as an angiosperm)
*'' Chengia'' Yang, Lin & Wang, 2013, Yixian Formation, China, Early Cretaceous (Aptian)
*''Chaoyangia
''Chaoyangia'' is an extinct genus of euornithean birds, containing the single species ''Chaoyangia beishanensis''. This species is known from a single fossil specimen consisting of a partial skeleton including vertebra, ribs, hips, and upper l ...
'' Duan, 1998 Yixian Formation, China, Early Cretaceous (Aptian)
*'' Eragrosites'' Yixian Formation, China, Early Cretaceous (Aptian)
*'' Gurvanella'' China, Mongolia, Early Cretaceous
*'' Alloephedra'' China, Early Cretaceous
*'' Amphiephedra'' China, Early Cretaceous
*'' Beipiaoa'' China, Early Cretaceous
*'' Ephedrispermum'' Portugal, Early Cretaceous (Aptian-Albian)
*'' Ephedrites'' China, Early Cretaceous
*'' Erenia'' China, Mongolia, Early Cretaceous
*'' Liaoxia'' China, Early Cretaceous
*'' Dichoephedra'' China, Early Cretaceous
Gnetaceae
*'' Khitania'' Guo et al. 2009 Yixian Formation, China, Early Cretaceous (Aptian)
Welwitschiaceae
*'' Priscowelwitschia'' Dilcher et al., 2005 Crato Formation
The Crato Formation is a geologic formation of Early Cretaceous ( Aptian) age in northeastern Brazil's Araripe Basin. It is an important Lagerstätte (undisturbed fossil accumulation) for palaeontologists. The strata were laid down mostly duri ...
, Brazil, Early Cretaceous (Aptian)
*'' Cratonia'' Rydin et al., 2003 Crato Formation, Brazil, Early Cretaceous (Aptian)
*'' Welwitschiostrobus'' Dilcher et al., 2005 Crato Formation, Brazil, Early Cretaceous (Aptian)
''Incertae sedis'':
*''Drewria
''Drewria potomacensis'' is a Cretaceous megafossil member of the Gnetales, from the Potomac Group, hence its name. It was possibly a shrub.Crane, Peter R., and Garland R. Upchurch Jr. "Drewria potomacensis gen. et sp. nov., an Early Cretaceous ...
'' Crane & Upchurch, 1987 Potomac Group
The Potomac Group is a geologic group in Delaware, Maryland, New Jersey, and Virginia. It preserves fossils dating back to the Cretaceous period. An indeterminate tyrannosauroid and '' Priconodon crassus'', a nodosaurid, are known from indetermi ...
, USA, Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
(possible affinities to Welwitschiaceae)
*'' Bicatia'' Friis, Pedersen and Crane, 2014 Figueira da Foz Formation, Portugal, Early Cretaceous (late Aptian early Albian), Potomac Group
The Potomac Group is a geologic group in Delaware, Maryland, New Jersey, and Virginia. It preserves fossils dating back to the Cretaceous period. An indeterminate tyrannosauroid and '' Priconodon crassus'', a nodosaurid, are known from indetermi ...
, USA, Albian (possible affinities to Welwitschiaceae)
*'' Liaoningia'' Yang et al, 2017 Yixian Formation, China, Early Cretaceous (Aptian)
*'' Protognetum'' Y. Yang, L. Xie et D.K. Ferguson, 2017 Daohugou
The Haifanggou Formation (), also known as the Jiulongshan Formation (), is a fossil-bearing rock deposit located near Daohugou () village of Ningcheng County, in Inner Mongolia, northeastern China.
The formation consists of coarse conglomerates ...
, China, Middle Jurassic (Callovian
In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma (million years ago) and 163.5 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...
)
*'' Itajuba'' Ricardi-Branco et al, 2013, Crato Formation, Brazil, Early Cretaceous (Aptian)
*'' Protoephedrites'' Rothwell et Stockey, 2013 Canada, Valanginian
In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretaceou ...
(possible ephedroid affinities)
*'' Siphonospermum'' Rydin et Friis, 2010 Yixian Formation, China, Early Cretaceous (Aptian)
*'' Welwitschiophyllum'' Dilcher et al., 2005 Crato Formation, Brazil, Early Cretaceous (Aptian), Akrabou Formation, Morocco, Late Cretaceous (Cenomanian
The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...
-Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...
) (Initially interpreted as a member of Welwitschiaceae, later considered uncertain).
*'' Dayvaultia'' Manchester et al. 2021 Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic, Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandsto ...
, USA, Late Jurassic (Tithonian
In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by the K ...
)
Possible gnetophytes (not confirmed as members of the group)
*'' Archaestrobilus'' Trujillo Formation, Texas, United States, Upper Triassic
*'' Dechellyia''-'' Masculostrobus'' Mongolia, Early Cretaceous (Aptian-Albian)
*''Dinophyton
''Dinophyton'' is an extinct genus of gymnosperm found in late Triassic beds in North America. Its taxonomy is debated, but it may be a gnetophyte with bisaccate pollen
Pollen is a powdery substance produced by seed plants. It consists of ...
'' Chinle Formation
The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...
, United States, Upper Triassic
*'' Nataligma'' Molteno Formation
The Molteno Formation is a geological formation found in several localities in Lesotho and South Africa. It lies mainly south of Maseru, near Burgersdorp, Aliwal North, Dordrecht, Molteno, and Elliot. It extends as far north as Matatiele in the ...
, South Africa, Upper Triassic (Carnian)
*'' Palaeognetaleana'' Wang, 2004, China, Upper Permian
*'' Sanmiguelia'' United States, Late Triassic-Early Jurassic
*'' Eoantha'' Russia, Early Cretaceous
*'' Bassitheca'' Morrison Formation, USA, Late Jurassic (Tithonian)
References
Other Sources:
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{{Taxonbar, from=Q309147
Plant divisions
Extant Permian first appearances